A Record-High Cryogenic Magnetocaloric Effect Discovered in EuCl<sub>2</sub> Compound
Bingjie Wang, Xin‐Yang Liu, Fengxia Hu, Jian-Tao Wang, Jian-Tao Wang, Junsen Xiang, Peijie Sun, Jing Wang, Jing Wang, Jirong Sun, Tongyun Zhao, Zhaojun Mo, Jun Shen, Yunzhong Chen, Q. Huang, Baogen Shen
Abstract
Adiabatic demagnetization refrigeration (ADR) based on the magnetocaloric effect (MCE) is a promising technique to achieve cryogenic temperature. However, magnetic entropy change (Δ S M ), the driving force of ADR, remains far below theoretical −Δ S M = nR ln(2 J + 1)/ M W for most magnetic refrigerants. Here, we report giant MCE in orthorhombic EuCl 2, where a ferromagnetic ground state with excellent single-ion behavior of Eu 2+ and free spins has been demonstrated by combining ab initio calculations with Brillouin function analysis and magnetic measurements. Consequently, a record-high −Δ S M ∼ 74.6 J·kg –1 ·K –1 (1.8 K) at 5 T was experimentally achieved, approaching 96% of the theoretical limit (77.5 J·kg –1 ·K –1 ). At a lower field of 1 T, EuCl 2 also achieves the highest-ever record of −Δ S M ∼ 36.8 J·kg –1 ·K –1 . Further, direct quasi-adiabatic demagnetization measurements demonstrate that its large −Δ S M allows EuCl 2 to maintain a long holding time at sub-Kelvin temperature (∼346 mK), surpassing all previously reported materials. These superior magnetocaloric performances position EuCl 2 as an attractive cryogenic refrigerant.